Well there's definitely something that they're liking in that area. Acorns most likely. If you can try and snoop on them once in a while. Be there before fly-down and you'll see when they hit that area. Hens will feed all day until they lay their eggs. After they've laid their eggs they'll feed in the morning and then go sit on the nest mid-morning or so. Once this happens, if you haven't got your bird yet, sit in those leaves and make some scratching sounds and if you can throw in some purrs and clucks you'll have a bird soon enough.